1. Field of the Invention
The present invention relates to pigment dispersing agents. More specifically, the present invention relates to a pigment dispersing agent comprising a phosphate ester salt having ethoxylated alkylphenol groups.
2. Description of the Related Art
After a pigment has been manufactured, typically it is formed into a presscake. The pigment presscake may then be dispersed in a dispersing medium. The dispersing medium is either a resin-based system, or an aqueous-based system which is commonly referred to as a surfactant-based system.
Resin-based systems, however, have several general drawbacks. Specifically, resin-based systems have a higher viscosity, thus presenting problems for example in handling. Resin-based systems also exhibit poor compatibility with aqueous pigment dispersions which are often used to impart color to a final product. Also, the resin-based systems encounter disposal problems requiring expensive disposal processes. Presently with particular pigments, however, resin-based systems have been exclusively employed because surfactant-based systems exhibit poor stability. These pigments in particular are: barium lithol; calcium lithol; and lithol rubine.
As mentioned, pigment may be dispersed in surfactant-based systems. In a surfactant-based system the pigment is dispersed in water. A surfactant-based system is not available for barium lithol, calcium lithol or lithol rubine because these pigments exhibit poor stability in this type of system. Specifically, the pigments gel upon storage.
Accordingly, a surfactant-based system which provides both long term storage, and short term storage (at elevated temperatures as is commonly experienced in transportation of the pigment) for these types of pigments is not known, and would be useful for all pigments in general.